The invention relates to a charging device for production of layers of fine-grained loose material one above the other on a rotary hearth. It is particularly suitable for the use of a new direct iron ore reduction process in a rotary hearth furnace.
Sponge iron is produced in a direct reduction process by the reduction of iron oxide with solid or gaseous reducing agents. Carbon, for example, which reacts with oxygen at higher temperatures and forms the reducing gas CO, serves as a solid reducing agent. A process of this type can be carried out, for example, in a rotary hearth furnace, i.e. in a furnace with a rotatable annular furnace bottom, which is lined with refractory material on the top side and is enclosed by a housing. Burners, which penetrate the housing and heat its interior to the required reaction temperature of over 1000.degree. C., are mounted on the top side of the housing.
The iron oxide is deposited together with the reducing agent at a first point of the rotary hearth furnace and is fed by rotation of the rotary hearth to the interior of the housing, where it reacts with the reducing agent because of the high temperatures and is present as directly reduced iron after about one revolution of the rotary hearth. The form in which the iron is present depends on the type of process used.
In the traditional process the iron oxide is compacted before charging into the rotary hearth furnace with the reducing agent to form pellets, which are subsequently charged on to the rotary hearth of the furnace. Inside the furnace, the iron oxide in the individual pellets reacts with the carbon monoxide released by the carbon in a controlled atmosphere and is reduced to iron inside the pellets. The sponge iron is thus present in pellet form after the reduction. The pellets additionally containing the residues of the reducing agent (ash) as well as any impurities such as sulphur. After the reduction process a further process step, in which the directly reduced iron is separated from the ash and impurities, is consequently required.
In an alternative process fine-grained iron oxide and fine-grained reducing agent, e.g. coal, are charged in separate layers on to the rotary hearth of the furnace. In this process only one layer of iron oxide and one layer of reducing agent can be charged or several layers of the individual materials can be placed alternately in layers one above the other. On passage through the furnace carbon monoxide, which penetrates through the fine-grained iron oxide layers and reduces them to iron, is released in the coal layer(s). Consequently the reduced iron is present in a pure form in one or more layers above each other after the reduction process, the individual iron layers being separated from each other by layers of reducing agent residues and these ash layers being present in loose form.
As the individual layers of loose material do not mix with each other during the reduction process, this process offers the advantage that the sponge iron and reducing agent residues can easily be separated from each other. The basic prerequisite for economic implementation of this reduction process, however, is that the charging device of the rotary hearth furnace is capable of producing an optimum layered arrangement of the metal oxide and reducing agent on the rotary hearth. Consequently a task of the invention is to create a rotary hearth furnace, the charging device of which largely meets this prerequisite.